Madrid is 3.5 hours behind Chennai
Best overlap: 11:30 AM to 6:30 PM in Chennai is 8:00 AM to 3:00 PM in Madrid.
Target 11:30 AM to 6:30 PM in Chennai, which lands at 8:00 AM to 3:00 PM for the Madrid side. Madrid is 3.5 hours behind Chennai, but you'd hardly notice — 7 hours of shared hours makes this feel like working in neighbouring time zones. For part of the year the maths changes: Madrid observes daylight saving, Chennai does not, shifting the overlap by an hour.